Operational ampifiers have seen widespread application in recent years. One of the major challenges to designers of operational amplifiers has been providing a suitable compromise on design parameters to yield an amplifier that can be utilized in multiple applications. One parameter of an operational amplifier, common-mode range, tends to present a major problem to designers since it is classically traded against common-mode rejection. In general, a fairly high common-mode rejection is desirable in a given amplifier. However, this high common-mode rejection is only attainable through the use of cascode devices which severely limit the common-mode range.
One problem with a cascode amplifer lies in the DC bias conditions for the output circuitry and also with the input circuit that must operate rail-to-rail. The DC bias problems in the output circuit result from the particular configurations utilized in differential to single-ended conversion circuits that are presently available. One such circuit is illustrated in Laber, Rahim, Dreyer, Uehara, Kwok and Gray, "Design Considerations for a High-Performance 3-.mu.m CMOS Analog Standard-Cell Library", IEEE Journal of Solid-State Circuits, Vol. SC-22, No. 2 (April 1987) pp. 181, 186. The device illustrated in this article illustrates common-mode range to only one rail.